1. Field of the Invention
The present invention relates to a plasma processing apparatus, and more specifically, relates to a plasma processing apparatus capable of subjecting a semiconductor device formed on a substrate using corrosive gas, and a plasma processing apparatus capable of processing a sample stably without causing heavy-metal contamination of the surface of the sample.
2. Description of the Related Art
A plasma processing apparatus utilizing plasma is widely used for manufacturing semiconductor devices. Especially, in a plasma etching process for forming semiconductor circuit structures, process gases containing halogen-based substances having high reactivity to silicon (hereinafter referred to as Si) compounds and aluminum (hereinafter referred to as Al) alloy and the like constituting the circuits are used. Therefore, alumite-treated aluminum (anodized aluminum) and stainless steel having high resistance to process gases have been used in general as the components constituting the processing chamber in which plasma is generated.
FIG. 9 illustrates a typical example of the arrangement of a prior art plasma processing apparatus. The processing apparatus comprises a lower electrode 104 for placing a wafer 103 within a processing chamber 101 capable of having its interior vacuumed, and a high-frequency electrode 102 for generating plasma 102 is attached via an insulating body 108 to the processing chamber 101. Upon generating plasma 102, the process gas supplied from a gas supply means 105 is supplied into the processing chamber 101 via gas discharge holes 107 formed to a gas shower plate 106 disposed on a front side of the high-frequency electrode 120. The high-frequency radiation for generating plasma is generally an electromagnetic wave ranging from 13 MHz to a few hundred MHz, which is applied from a high-frequency power supply 110 via a matching box 109 to the high-frequency electrode 120, so as to irradiate an electric field required for discharge to the plasma.
For example, in a semiconductor manufacturing step for etching Si compounds, a halogen gas such as chlorine is fed to the processing chamber so that the gas pressure is maintained constantly within the range of approximately 0.1 Pa to 10 Pa, and high-frequency power for generating plasma ranging from a few hundred W to a few k W is applied to the high-frequency electrode 120. Moreover, in order to control the ion irradiation energy from the plasma to the wafer 103, normally a high-frequency radiation of a few hundred kHz to a few MHz is applied to the lower electrode 104, according to which the potential of the wafer 103 ranges between tens to hundreds of V, and the ions irradiated to the wafer 103 are accelerated.
Therefore, a high-frequency electric field of approximately a few hundred V is generated in the plasma-generating high-frequency electrode 120 and the wafer 103, and the surface of the high-frequency electrode 120, especially the surface of the gas shower plate 106, and the inner surface of the processing chamber 101 coming into contact with plasma 102 are subjected to sputtering by ions irradiated from plasma and attaching of reactive radicals, and therefore, are susceptible to corrosion. Generally, in order to cope with this problem, an Al treated with hard alumite (anodized aluminum) coating or stainless steel (hereinafter referred to as SUS) are used as the base material for forming the high-frequency electrode 120 and the processing chamber 101 (refer for example to Japanese Patent Application Laid-Open Publication Nos. 2004-190136 and 2003-243372, hereinafter referred to as patent documents 1 and 2), or the surface exposed to plasma is partially coated by spraying ceramic material.
However, during mass production processes performed continuously for a long period of time in factories and the like, the load of heat flow cycles caused by plasma discharge cycles of plasma 102 ranging between a few hundred W to a few k W is applied on the surface of the high-frequency electrode 120 and the processing chamber 101 exposed to plasma 102. Therefore, the aluminum base material is subjected to thermal contraction, causing the alumite coating to be cracked and removed, and the base material is corroded through the cracked portion, causing the device to be contaminated by the small amount of heavy-metal compounds such as iron (hereinafter referred to as Fe), magnesium (hereinafter referred to as Mg) and chrome (hereinafter referred to as Cr) contained in the base material, or causing defective circuit pattern by the small particles generated by corrosion. Such metal contamination can be reduced by using a high-purity material containing very little heavy metal as the spraying material for creating a ceramic sprayed film having a relatively thick film thickness (approximately a few hundred μm). However, high cost is required for performing a spraying process using high-purity material, and the sprayed film has a drawback in that when it is used as the surface protecting film of a high-frequency electrode 120 applying high-power radiation, it is susceptible to consumption by ion sputtering and the life thereof is short.
Along with the recent miniaturization of semiconductor devices, the permissible level of metal contamination and quantity of generated particles has become stricter, so it has become difficult according to the prior art to achieve the permissible level of heavy-metal contamination caused by the high-frequency electrode and the processing chamber and the quantity of particles caused by reactive gas corrosion. Especially, the surface of the high-frequency electrode is damaged significantly via plasma ion sputtering in the high-power high-frequency electric field, so the most important problem to be solved is to prevent damage of the high-frequency electrode and significantly reduce generation of heavy metal and particles from the base material constituting the electrode. At this time, the high-frequency electrode enables to generate uniform high-density plasma by applying a high-frequency electric field to the plasma in a uniform and efficient manner, so it is important to ensure the effective properties of the electrode related to the propagation of the high-frequency electric field and the interaction of the electric field with plasma. Furthermore, by feeding process gas uniformly toward the wafer, it becomes possible to process the whole surface of the wafer uniformly by controlling the generation and flow of active radicals causing chemical reaction. Therefore, there were demands for a plasma processing apparatus with reduced heavy-metal contamination and corrosion by radicals, and at the same time capable of sufficiently satisfying the performance of processes and plasma generation.